The conversion of standards, or more generally the conversion of frame frequency, usually relies on two types of processes:                movement estimation, which supplies a movement-vectors field which is faithful to the space/time changes in the objects which constitute the scene,        interpolation, which can make use of this vector field in order to position the objects correctly in an intermediate frame to be constructed.        
Linear or movement-compensated interpolations, which are conventionally applied in frame-frequency conversion, are not always suitable for all the situations encountered in a video sequence. It is sometimes necessary to deal with critical situations which cause difficulty for the estimator or interpolator, by making use of appropriate detection which can invoke a more suitable interpolation configuration.
This is because, in theory, a movement-vectors field is temporally uniform over a video sequence. A movement-vectors field, when it is correct, undergoes very little time-domain variation. A time-domain irregularity is often synonymous with an unreliable movement-vectors field. When an abnormal variation occurs, denoting a movement estimation with a time-domain disturbance, movement-compensated interpolation may give a poor-quality image.
Consequently, when an instability is detected in the time domain, suggesting that the video content is incompatible with movement estimation, it is necessary to opt for a frame-interpolation process other than that making use of the movement-vectors field.
The object of the proposed invention is to resolve such problems, by making it possible to evaluate the reliability of the movement-vectors field.